The present invention relates to a method and apparatus for transferring an image of an original to photosensitive material.
Current plate making practice in many printing plants is to make a paste-up copy which is photographed to produce a full sized image on film as a negative. The silver halide film must be developed in a separate processor. The developed film negative then must be placed in contact with the unexposed plate in a vacuum frame. The plate is then exposed to high intensity ultraviolet radiation which causes a photochemical reaction to take place on the surface of the plate. The film is then removed and the plate is further prepared by developing (offset lithography) or wash out (letterpress/flexo) operation.
Another known method of making printing plates includes providing a plate which is coated with an organic photoconductive layer. The photoconductive layer is charged and then exposed to a paste-up copy which is projected onto the plate surface. Background areas of the image reflect light and discharge the plate. As soon as the plate exposure is finished, the plate is moved into a processor where a liquid dispersant containing positively charged toner particles is applied to the surface of the plate. The toner particles adhere to negatively charged areas of the plate. After being dried, the toner particles on the plate are fused together and bonded to the surface of the plate. After decoating, rinsing and gumming, the plate is ready for use in a printing press.
The consumable materials used in these known processes are relatively expensive. Thus, silver halide film in full size is expensive as are chemicals used in developing it. If electrostatic plates are used, they are relatively expensive compared to conventional offset plates. In addition, these known processes are relatively slow in going from paste-up to completed plate. The quality of the image obtained on the completed plate, although it may be considered as being acceptable, may be of lesser quality than desired. In the addition, the apparatus used to practice these known processes requires a relatively large amount of space and is difficult to automate so that it can be operated with a minimum of personnel.